Creatures
Animals (or Metazoa) are living creatures with many cells that make up the kingdom Animalia.
Animals get their energy from other living things. Usually, they eat them or are parasites. Animals, plants, fungi, and some other living things have complex cells, so they are grouped together as eukaryotes.
The study of animals is called zoology. The study of ancient life is called palaeontology.
Most animals are mobile, meaning they can move around. Animals take in oxygen, and give out carbon dioxide. This cellular respiration is part of their metabolism (chemical working). In both these ways they are different from plants. Also, the cells of animals have different cell membranes to other eukaryotes like plants and fungi.
Plants are also multicellular eukaryotic organisms, but live by using light, water and basic elements to make their tissues.
Grouping animals
There are many different types of animals. The common animals most people know are only about 3% of the animal kingdom. When biologists look at animals, they find things that certain animals have in common. They use this to group the animals in a biological classification. Several million species may exist, but biologists have only identified about one million.
Animals can mainly be divided into two main groups: the invertebrates and the vertebrates. Vertebrates have a backbone, or spine; invertebrates do not. Vertebrates are the only group to have an adaptive immune system, which may be partly responsible for their size and success.
Vertebrates are:
- Fish (or ‘fishes’: both ways are correct)
- Amphibia
- Reptiles
- Birds
- Mammals
Some invertebrates are:
- Insects
- Spiders
- Crustacea
- Molluscs (like a snail or squid)
- worms
- jellyfish
Life styles
The animal mode of nutrition is called heterotrophic because they get their food from other living organisms. Some animals eat only plants; they are called herbivores. Other animals eat only meat and are called carnivores. Animals that eat both plants and meat are called omnivores. Some animals get their energy from photosynthetic protists that live inside them.
The environments animals live in vary greatly. By the process of evolution, animals adapt to the habitats they live in. A fish is adapted to its life in water and a spider is adapted to a life catching and eating insects. A mammal living on the savannahs of East Africa lives quite a different life from a dolphin or porpoise catching fish in the sea.
The fossil record of animals goes back about 600 million years to the Ediacaran period, or somewhat earlier. During the whole of this long time, animals have been constantly evolving, so that the animals alive on Earth today are very different from those on the edges of the sea-floor in the Ediacaran.
Written for younger readers
Creatures, in simpler words
This version comes from Wikijunior, a set of books written for children aged 8 to 11. It is shorter and uses plainer language than the article above.
From Wikijunior: Biology
NOTOC
Many different creatures live on earth: plants, insects, birds, fish, bacteria, humans and many more. They have many differences and similarities.
File:Monkey of kembang island.jpg|thumb|Monkey File:Pterois volitans Manado-e edit.jpg|thumb|Pterois volitans File:Marabou Stork at Animal Kingdom Lodge.jpg|thumb|Marabou Stork File:Jelly Monterey.jpg|thumb|Jellyfish File:Common carder bee.jpg|thumb|Common carder bee File:Euglena.gracilis.jpg|thumb|Euglena
According to the theory of evolution, all living beings on earth are related to each other.
We humans are therefore related to monkeys, cows and apple trees, but also to mosquitoes and bacteria. All living organisms on earth today share common ancestors.
File:Tree of life by Haeckel.jpg|thumb|Tree of life by Haeckel File:Circular timetree-of-life 2009.jpg|thumb|ohne|Circular timetree-of-life 2009 In 1879, the biologist Ernst Haeckel drew a family tree of living things inspired by the family trees of noble families. At the roots are the unicellular organisms, from which all higher living beings descend, with humans at the top. Scientists are aware that scientific statements can be wrong and therefore look for errors. They found errors in Haeckel’s picture. So, the birds are drawn in the wrong place.
Modern family trees are much more complex. Humans are now on a par with other living organisms. On the left of the picture are the mammals, next to them are the birds. One of the lines denotes the humans. Extinct creatures such as dinosaurs are not shown here. Even the modern family trees are probably wrong. Viruses can transfer genes between different organisms and protozoa can exchange genes with other protozoa. There are many unanswered questions, especially in the case of unicellular organisms. There is still much to explore for future biologists.
Where this page comes from
The article above is adapted from “Creatures” on Simple English Wikipedia, by its contributors. We removed reference markers, navigation boxes and tables, expanded measurement templates into readable numbers, and kept the prose otherwise intact. The simpler version is adapted from Wikijunior on Wikibooks.
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